Of course, it requires a bit more than just the standard library. ;) This has a couple extra nice features though - it does logging, for example, and it can be trivially daemonized, or run under the profiler or the debugger, or chrooted or as a different uid/gid. Plus the Foo resource can easily be relocated into a "real" program, since it is entirely distinct from the HTTP server part of the code.

There's an even simpler way to express this though, as an rpy instead of a tac:

from twisted.web.resource import Resource

class Foo(Resource): def render(self, request): return "hello world"

resource = Foo()

Just drop this into a directory and run a Twisted web server pointed at it (eg, twistd web --processor rpy=twisted.web.script.ResourceScript --path bar/). You can even change the code without restarting the server if you do it this way. rpys can be convenient for one-off hacks, but clearly it's not suitable for anything larger scale than that.